Abstract

Observers adjusted a probe (a short rod) to appear normal to a planar surface slanted in depth. In Experiment
1, observers (N = 12) performed this metric task in two conditions: with reduced cues to calibration
of binocular viewing parameters and with full cues. The results provided evidence for the use of an internal
working metric in metric tasks because they confirm predictions that (i) errors should be largely systematic
and accounted for by assuming an inaccurate working metric and (ii) this metric should be
consistent with miscalibration of relevant viewing parameters. The data support the prediction that performance
errors decrease in a manner consistent with improved binocular calibration, when better cues
to relevant viewing parameters are provided. We performed two additional control experiments as further
tests of the binocular miscalibration account, to determine whether performance in Experiment 1
could be explained instead by the use of monocular cues. We found that monocular performance was significantly
poorer than binocular performance in reduced-cue conditions (Experiment 2) and full-cue conditions
(Experiment 3). These control experiments provide confirmation that binocular cues contribute to
performance in the full-cue conditions of Experiment 1, and that disparity was the only effective cue to
slant in reduced-cue conditions.